Time information obtaining device and radio-controlled timepiece

ABSTRACT

A time information obtaining device and a radio-controlled timepiece are shown. According to one implementation, the time information obtaining device includes a noise determining section and a reception cancelling section. The noise determining section determines whether noise mixed in a demodulated signal of a radio wave received within a predetermined unit of time is equal to or more than a predetermined threshold level. The reception cancelling section cancels reception of the radio wave when a number of times that the noise determining section determines that the noise mixed in the signal is equal to or more than a predetermined level is included at a percentage equal to or more than a predetermined percentage within a set time including a plurality of the units of time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a time information obtaining device anda radio-controlled timepiece.

2. Description of the Related Art

Conventionally, there is an electronic timepiece which receives a radiowave including time information, and automatically calibrates the timeso as to be able to maintain display of the accurate time. As a radiowave which includes the time information, there is an airwave called astandard radio wave which transmits encoded time information with aradio wave in a long wavelength band. Various electronic timepieces(radio-controlled timepieces) which receive such standard radio wave toobtain time information are being developed.

The radio wave in the long wavelength band is transmitted long distancesthroughout the surface of the Earth. Therefore, it is possible toreceive and use the standard radio wave at a point far from atransmission station. However, noise which is generated in the samewavelength band is also similarly transmitted long distances. Moreover,the radio wave attenuates inside a building made of a steel frame orreinforced concrete. Therefore, various techniques to enhance receivingsensitivity and to cope with noise are being developed inradio-controlled timepieces.

Specifically, in an electronic timepiece where the power capacity issmall due to weight and size as in a watch, since the power consumedwhen the radio wave is received is very large, a technique is developedto promptly cancel or interrupt reception when the state of reception isbad and it is unlikely that the time information can be obtained. Forexample, Japanese Patent Application Laid-Open Publication No.2012-189558 discloses a technique to judge the radio wave receptionintensity based on AGC (automatic gain control) voltage or a techniqueto judge noise intensity based on degree of accuracy of deciding theposition of change of the signal (amplitude) intensity.

However, if the noise is mixed at an important timing for determiningthe code when the standard radio wave is received, it becomes difficultto determine the code. When the noise mixed in the standard radio waveis a sudden noise (burst noise) instead of continuous noise,conventional methods cannot accurately judge the influence of the noiseto judge whether to continue or cancel reception of the radio wave.

The present invention is a time information obtaining device and aradio-controlled timepiece which can more accurately judge whether ornot to obtain time information and which can cancel the reception of theradio wave during the reception.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided atime information obtaining device which receives a radio wave includingtime information to obtain time information, the time informationobtaining device including:

a noise determining section which determines whether noise mixed in ademodulated signal of a radio wave received within a predetermined unitof time is equal to or more than a predetermined threshold level; and

a reception cancelling section which cancels reception of the radio wavewhen a number of times that the noise determining section determinesthat the noise mixed in the signal is equal to or more than apredetermined level is included at a percentage equal to or more than apredetermined percentage within a set time including a plurality of theunits of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and the above-described objects, features andadvantages thereof will become more fully understood from the followingdetailed description with the accompanying drawings and wherein;

FIG. 1 is a block diagram showing an internal configuration of anelectronic timepiece of an embodiment of the present invention;

FIG. 2 is a diagram describing a code array of JJY;

FIG. 3 is a flowchart showing a control procedure of time informationobtaining processing in an electronic timepiece of a first embodiment;

FIG. 4 is a flowchart showing a processing procedure of noise measuringprocessing;

FIG. 5 is a block diagram showing an internal configuration of anelectronic timepiece of a second embodiment; and

FIG. 6 is a flowchart showing a control procedure of time informationobtaining processing of an electronic time piece of a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, an embodiment of the present invention is described withreference to the drawings.

FIG. 1 is a block diagram showing an internal configuration of anelectronic timepiece 1 of an embodiment of the present invention.

The electronic timepiece 1 is a radio-controlled timepiece which canreceive a standard radio wave to calibrate the time. The electronictimepiece 1 can be a portable watch or a pocket watch, or a table clockor a wall clock.

The electronic timepiece 1 includes a display section 31 (time displaysection), a display driver 32 which drives the display section 31, anantenna 33, a radio wave receiving section 34 (receiving section) whichreceives a radio wave through the antenna 33, a CPU (Central ProcessingUnit) 41 (a noise determining section 410, a reception cancellingsection 411, a signal change counting section 410 a, a mixed noisedetermining section 410 b, a code identifying section 412, a majoritydeciding section 413, a time calibrating section 414), a ROM (Read OnlyMemory) 42, a RAM (Random Access Memory) 43, an oscillating circuit 44,a frequency dividing circuit 45, a time keeping circuit 46 (time keepingsection), a power source section 47, an operation section 48, and thelike.

For example, the display section 31 is a digital display sectionincluding a liquid crystal display section of a dot matrix type, and thedisplay driver 32 is a liquid crystal display driver. The displaysection 31 can use a liquid crystal display of a segmented method or canuse other digital display types such as an organic EL(electro-luminescent) display. The display driver 32 is a display driverwhich is driven in a method corresponding to the type of display used inthe display section 31.

Alternatively, the electronic timepiece 1 can be an analog display typeelectronic timepiece including a rotating display section such as aplurality of needles as the display section 31. The rotating displaysection can be rotated through an array of gears driven by a step motor.

The antenna 33 and the radio wave receiving section 34 receive a radiowave with a long wavelength band, amplify and detect an amplitudemodulated wave and demodulates a signal from the standard radio waveincluding time information. The radio wave receiving section 34 isconfigured to be able to synchronize with the reception frequencyselected from among the frequencies of the plurality of standard radiowaves set in advance. The radio wave receiving section 34 may include abinarizing section 340 including a comparator 340 a and ananalog/digital convertor (ADC) 340 b. The binarizing section 340binarizes the obtained signal to a high-level signal or a low-levelsignal according to a predetermined threshold level (binarizingthreshold level) to output the signal to the CPU 41 at a predeterminedsampling frequency (for example, 64 Hz). The data can be binarized at anactive low so that the signal is to be a low level in a term when theamplitude is large and the signal is to be a high level in a term whenthe amplitude is small. By setting the intensity of the amplified anddemodulated signal to be as even as possible using the AGC, it ispossible to standardize the input signal level with respect to thethreshold level for determining the boundary between the high-levelsignal and the low-level signal.

The CPU 41 performs various calculating processing and centrallycontrols the entire operation of the electronic timepiece 1. When theelectronic timepiece 1 is started, the CPU 41 reads a control programfrom the ROM 42 and executes the program. With this, the CPU 41 performsprocessing regarding continuously counting the time and displaying thetime. Moreover, the CPU 41 operates the radio wave receiving section 34at a regular interval such as once a day to receive the standard radiowave, and calibrates the time. The time information obtaining device iscomposed of the above described antenna 33, the radio wave receivingsection 34, and the CPU 41.

Various programs and setting data are stored in the ROM 42. Included inthe various programs is a decrypting program to decode and obtainaccurate time information from the demodulated standard radio wavesignal. The ROM 42 includes a model array storage section 42 a whichstores 10 model arrays (in other words, the first one minute unit digitis any one of 0 to 9) to calculate a degree of match with the code arrayof 12 codes arranging in order 3 groups of 4 codes showing the oneminute unit digit which can be obtained from the code array of 3consecutive minutes (3 frames).

The RAM 43 provides a work memory space in the CPU 41 and storestemporary data. The RAM 43 includes a code data storage section 43 awhich can store code data for a plurality of identified frames.

The oscillating circuit 44 is a circuit which generates and outputs afrequency signal, and for example, a crystal oscillator is used. Thefrequency dividing circuit 45 divides and outputs a signal input fromthe oscillating circuit 44 to a signal with a frequency used in eachsection such as the CPU 41 and the time keeping circuit 46. The timekeeping circuit 46 counts the number of times a predetermined frequencysignal is input from the frequency dividing circuit 45 and adds thenumber to a preset initial time to count the present time.

The power source section 47 supplies predetermined electric powernecessary for the operation of the CPU 41 and the display driver 32. Forexample, the power source section 47 includes a solar battery or asecondary battery and is able to supply electric power continuously fora long period of time.

The operation section 48 includes a pressing button or a winding crownto accept operation from outside. The accepted operation is converted toan electric signal, and the electric signal is output to the CPU 41. Theoperation section 48 may include a detecting sensor for a touch panel,and the display screen of the display section 31 may be used as a touchpanel.

Next, the codes included in the standard radio wave and theidentification of the codes are described.

In the example described below, the time information is obtained fromthe standard radio wave signal of JJY which is the standard radio wavetransmission station of Japan. However, time information can also besimilarly obtained from other standard radio wave signals by selectingand using a suitable encoding format.

According to JJY, the time information is represented by three types ofcodes (time code) showing “0”, “1”, and “P” in an array according to apredetermined format, and the code array signal regarding the timeinformation is modulated and transmitted. The three types of codes aredistinguished according to the length of the term with a large amplitudewhich is started synchronized with the start of the timing of eachsecond (second synchronizing point). In other words, the code “0” isshown when a term with a predetermined amplitude (high level term)continues for 0.8 seconds and then a term with an amplitude of 10% ofthe above amplitude (low level term) continues for 0.2 seconds. The code“1” is shown when a term with a predetermined amplitude continues for0.5 seconds and then a term with an amplitude of 10% of the aboveamplitude continues for 0.5 seconds. The code “P” is shown when a termwith a predetermined amplitude continues for 0.2 seconds and then a termwith an amplitude of 10% of the above amplitude continues for 0.8seconds.

Each of the above codes can be identified by detecting the timing thatthe amplitude changes from the large state to the small state in eachsecond of the demodulated signal (timing of a falling edge of a signalintensity). As described above, such timing of the falling edge is anyone of 0.2 seconds, 0.5 seconds, or 0.8 seconds. Therefore, it ispossible to read which code the code is by directly or indirectlyidentifying which one of the above the code is. Various known methodscan be used as the specific methods including techniques to enhance theaccuracy of identification. A code string for 1 frame in which 60identified codes showing 60 seconds are arranged is decoded according toa predetermined format to obtain the time information.

FIG. 2 is a diagram describing a code array of data of 1 frame of JJY.

In the standard radio wave of JJY, the code “P” is transmitted fixed asa position marker showing a timing when the value of the one second unitdigit is “9” and as a marker showing a timing of the start of eachminute (00 seconds). The codes “0” and “1” transmitted in other timingshow the content of the time information. Binary Coded Decimal is usedfor the display of the value of the time and date. The values showingten minute unit digit, one minute unit digit, ten hour unit digit, onehour unit digit, hundred day unit digit, ten day unit digit, one dayunit digit, ten year unit digit and one year unit digit are each shownbinary of 2 to 4 bits. For example, the value of the ten minute unitdigit in the time of a certain minute is shown by the array of code dataof 3 codes transmitted in 1 to 3 seconds of each minute (3 bit data),and the value of the one minute unit digit in the time of a certainminute is shown by an array of code data of four codes transmitted in 5to 8 seconds of each minute (4 bit data).

As other contents of time information, there are day of week, paritydata for checking data, information showing when a leap second isinserted, and extended blocks for future use such as summer timeinformation. Among the above, other than the code array showing day ofthe week (3 bit data), the data is not always necessary for the displayof the time and the data. Therefore, after the position of the start ofeach minute is identified, as for the above codes and the code “P” whichis a total of 26 codes (24 codes when a parity check is performed), itmay not be a problem even if the codes cannot be identified due tonoise, etc.

Here, as described above, normally, the falling edge of the signalintensity appears once for each second showing one code. However, whenthe C/N ratio is bad due to low reception level, the rising edge timingand the falling edge timing of the signal intensity are not determinedaccurately, and the rising edge and the falling edge are detected aplurality of times in each second. Even if the reception level is high,when noise is mixed temporarily, the signal intensity temporarily risesduring the noise, and the rising edge and the falling edge of the signalmay be detected a plurality of times. If the number of the falling edgesand the rising edges of the signal intensity increases, it is notpossible to identify the code accurately. However, if the rising edgeand the falling edge are not detected, this means the signal intensityis too low to identify the code or the noise is continuously strong.Therefore, it is possible to judge the amount of influence from thenoise by counting the number of the falling edges (or the number of therising edges) in the signal for each second.

Next, the operation to obtain the time information performed in theelectronic timepiece 1 of the embodiment of the present invention isdescribed.

In the electronic timepiece 1 of the present embodiment, a signal of apredetermined amount of time set in advance (set time) such as 20seconds is synchronized to each second (unit of time) to be divided into20 pieces for each second. The number of falling edges in the signaldetected within the term is counted. Then, when it is judged that thecounted number is 0 or equal to or more than a predetermined threshold(equal, to or more than a threshold level), the second is counted as thenoise term. When the number of noise terms within the 20 seconds isequal to or more than the predetermined number, it is judged that it isdifficult to obtain accurate time information and the reception of thestandard radio wave is canceled during reception.

FIG. 3 is a flowchart showing a control procedure of the timeinformation obtaining processing performed by the CPU 41.

For example, the time information obtaining processing is processingwhich is called and automatically started at a preset time every day orprocessing which is started manually based on input operation to theoperation section 48 by the user.

When the time information obtaining processing is started, the CPU 41operates the radio wave receiving section 34 to start reception of thestandard radio wave and demodulation of the signal (step S101). Next,the CPU 41 obtains the demodulated signal from the radio wave receivingsection 34, and detects and defines the second synchronizing point fromthe wave pattern (step S102). As the method of defining the secondsynchronizing point, it is possible to use various well known methods.For example, in the time information obtaining processing, the CPU 41adds digital data sampled at a temporal resolution (for example, 32 Hz)high enough for the length (1 second) of each code for each piece ofdata at a same phase in a cycle of 1 second. As a result, the CPU 41 isable to identify the point in which the change of the intensity ofamplitude of the signal from the low level to the high level is mostdrastic as the second synchronizing point. The sampled digital data canbe binary data or multi-valued data.

When the second synchronizing point is identified, the CPU 41 starts theprocessing regarding the later described noise measurement (step S103).The processing regarding the noise measurement is processing performedparallel with the time information obtaining processing by the CPU 41.Then, the CPU 41 sequentially identifies the code from the signal ofeach second. The CPU 41 detects the point where the code “P” continuestwo times and defines the timing of the start of 0 second of each minute(minute synchronizing point) (step S104). For example, in the timeinformation obtaining processing, the CPU 41 obtains the averageamplitude intensity of each term by adding and averaging data of 0.2seconds to 0.5 seconds from the second synchronizing point and data of0.5 seconds to 0.8 seconds from the second synchronizing point among thedata sampled at the above high temporal resolution. Then, the CPU 41identifies the code based on whether the average amplitude intensity iscloser to the low level or the high level.

When the minute synchronizing point is detected, the CPU 41 judgeswhether a predetermined number of frames (here, 5 frames) of the codestring data is obtained (step S105). When it is judged that apredetermined number of frames of code string data is not yet obtained(step S105, “NO”), the CPU 41 obtains the signal of the next second,identifies the code, and stores the identified code corresponded withthe value of the second in the code data storage section 43 a (stepS106). Then, the processing of the CPU 41 returns to step S105.

When it is judged that a predetermined number of frames of code stringdata is obtained (step S105, “YES”), the CPU 41 decides the majorityamong the 3 codes identified in each second excluding the data portionshowing the one minute unit digit (5 seconds to 8 seconds) and the dataportion showing the minute unit parity (37 seconds) for the code stringdata of the first 3 frames from the code string data of the obtained 5frames. Then, the CPU 41 selects the code of the majority and obtainsthe time information based on the code string data generated as a resultof the above (step S107). The CPU 41 calculates the degree of matchbetween the code string of 12 codes consisting of the 4 codes showingthe one minute unit digit identified in 3 frames arranged in the orderof reception and the code string of 10 patterns stored in the modelarray storage section 42 a. Based on the 3 values of the one minute unitdigit shown by the matching or most similar code string, the CPU 41 setsthe value of the one minute unit digit of the obtained time information.

The processing of step S107 can be performed for the code each time thecode of the third frame is identified, or the code string each time thecode string of each digit in the time information of the third frame isobtained. Alternatively, the processing of step S107 can be performedparallel with the processing of receiving the signal and identifying thecode of the remaining 2 frames.

The CPU 41 obtains the time information from the code array of theremaining 2 frames, and the CPU 41 confirms the consistency between theobtained two pieces of time information and majority time informationobtained in the processing of step S107 (step S108). The CPU 41 judgeswhether the result of the confirmation shows that there is consistency(step S109). When it is judged that there is no consistency (step S109,“NO”), the CPU 41 advances the processing to step S110. The CPU 41erases the obtained data with no consistency and then returns theprocessing to step S105 to obtain the data again.

Here, the CPU 41 can erase the code string data of all 5 frames or ifthe code string data of only 1 frame is not consistent, the CPU 41 canerase only the code string data of the frame which is not consistent.Alternatively, the CPU 41 can erase the code string data of the oldestframe.

When it is judged that there is consistency (step S109, “YES”), the CPU41 sets the present time based on the time information with consistency,and the present time of the time keeping circuit 46 is overwritten andcalibrated (step S111). Then, the CPU 41 ends the noise measuringprocessing (step S112) and ends the time information obtainingprocessing.

FIG. 4 is a flowchart showing the processing procedure of the noisemeasuring processing called and performed parallel with the processingof step S103.

When the noise measuring processing starts, the CPU 41 first initializessetting (step S301). In other words, the CPU 41 holds the variable ofcounting the number of times the falling edge is counted in each secondand the number of noise terms in the RAM 43, and sets the number to theinitial value “0”.

Then, the data obtained in the predetermined sampling frequency from theradio wave receiving section 34 in the one second started bysynchronizing with the synchronizing point of each second is analyzed.The CPU 41 adds 1 to the number of times of the falling edge each timethe CPU 41 detects the change from the value showing that the signalintensity is strong (for example, “0” in the binary data of the activelow) to the value showing that the signal intensity is weak (forexample, “1” in the binary data of the active low) (step S302).

When one second passes, the CPU 41 judges whether the number of countedfalling edges in one second is “0” or equal to or more than thethreshold (step S303). When it is judged that the number is “0” or equalto or more than the threshold (step S303, “YES”), the CPU 41 adds 1 tothe number of counted noise terms (step S304), and advances theprocessing to step S305. When it is judged that the number is neither“0” nor equal to or more than the threshold (step S303, “NO”), theprocessing of the CPU 41 advances directly to step S305.

When the processing advances to step S305, the CPU 41 judges whether 20seconds have passed and the number of noise terms for 20 seconds isobtained. When it is judged that 20 seconds have not passed (step S305,“NO”), the processing of the CPU 41 returns to step S302 and theprocessing of steps S302 to S305 is repeated.

When it is judged that 20 seconds have passed (step S305, “YES”), next,the CPU 41 judges whether the obtained number of noise terms within 20seconds is equal to or more than the predetermined number (step S306).When it is judged that the number is not equal to or more than thepredetermined number (step S306, “NO”), the CPU 41 returns the countednumber of noise terms to 0 (step S307) and returns the processing tostep S302. Then, the CPU 41 repeats the processing of steps S302 toS306, and detects and counts the noise terms from 0 seconds. In otherwords, the CPU 41 detects and counts the noise terms in a cycle of 20seconds (predetermined amount of time).

When it is judged that the number is equal to or more than apredetermined number (step S306 “YES”), the CPU 41 displays that thereis an error in reception on the display section 31 and stores the abovein the RAM 43 (step S308). The CPU 41 cancels the reception of thestandard radio wave (step S309), and cancels the time informationobtaining processing. Then, the CPU 41 ends the noise measuringprocessing.

Here, as in the time information obtaining processing of the presentembodiment, when decision by majority is used for each code, it ispossible to obtain accurate information even if false determination ismixed once in three times for each code due to noise. Therefore, in thetime information obtaining processing, a value of about ⅓ of 20 seconds,in other words, a value equal to or more than 6 or 7 is set as the abovedescribed predetermined number. In practice, the noise may be mixed inthe code not necessary for obtaining the time information or the timingwhen the noise is mixed may not influence the identification of thecode. Therefore, it is possible to set the predetermined number to alarger number such as about 10.

As described above, the electronic timepiece 1 of the first embodimentincludes a radio wave receiving section 34 and an antenna 33 whichreceive a standard radio wave. The CPU 41 obtains the signal demodulatedby the radio wave receiving section 34, and counts the number of changesof the signal by the noise for each second of the signal. When thenumber of changes counted is equal to or more than a threshold or is 0,it is determined to be a noise mixed term, and when the number of timesdetermined to be a noise mixed term within 20 seconds is equal to ormore than a predetermined number, it is judged that obtaining timeinformation is difficult at this point, and the reception of thestandard radio wave is canceled. With such determination, it is possibleto accurately judge whether it is difficult to obtain time informationwhen the C/N ratio is continuously bad due to the reception radio waveintensity being low or the noise constantly overlapping. It is alsopossible to make an accurate judgment when it is difficult to identifythe code even when the noise is not large considering an average of howfrequent the noise is mixed discretely by burst noise mixed irregularly.As a result of the judgment, it is possible to efficiently preventunnecessary consumption of energy by cancelling the reception of theradio wave during reception when it is difficult to obtain the timeinformation.

The amount of noise mixed can be determined by simply detecting thechange of the signal level based on the predetermined threshold leveland counting the number of changes. Therefore, it is possible to easilyjudge how much the mixed noise influences the process of obtaining thetime information without performing complicated processing.

The amount of mixed noise is determined by counting the change amongbinary values after the demodulated signal is binarized using thecomparator 340 a and the ADC 340 b. Therefore, it is possible to judgethe amount of noise mixed by easy processing.

Whether the noise is mixed is judged for each second which is equal tothe length of each code in the standard radio wave. Therefore, it ispossible to easily and objectively determine the amount of signals whichmay be difficult to decrypt among the entire signals. Consequently, itis possible to judge whether to continue reception of the radio wave.

The judgment of how much the noise is mixed is continued repeatedly.Therefore, it is possible to accurately judge the amount of mixed noisegenerated suddenly and/or irregularly. Consequently, it is possible toreduce needless consumption of electric power.

By judging the degree of the mixed noise for each code, when the correctcode is decided by majority among a plurality of frames (for example, 3frames), it is possible to accurately judge whether the amount of mixednoise is a level which does not influence the result of the majority.Therefore, it is possible to decide whether to continue to obtain thetime information from the standard radio wave or to abandon obtainingthe time information at an early stage. Consequently, it is possible toreduce needless consumption of energy.

By including a configuration which can determine the amount of mixednoise in the electronic timepiece 1, it is possible to reduceconsumption of the battery of the electronic timepiece 1. Specifically,the above configuration enhances efficiency of reducing powerconsumption while maintaining accuracy of time in an electronictimepiece 1 such as a watch where there is a limit in the batterycapacity.

Second Embodiment

Next, the electronic timepiece 1 a of the second embodiment isdescribed.

FIG. 5 is a block diagram showing an internal configuration of theelectronic timepiece 1 a of the second embodiment.

The configuration of the electronic timepiece 1 a of the secondembodiment is the same as that of the electronic timepiece 1 of thefirst embodiment with the exception of the model array storage section42 a not being included in the ROM 42. The same reference numerals areapplied to the same components, and the description is omitted.

FIG. 6 is a flowchart showing the control procedure of the timeinformation obtaining processing in the electronic timepiece 1 a of thesecond embodiment.

The time information obtaining processing performed by the CPU 41 in theelectronic timepiece 1 a is the same as the time information obtainingprocessing performed by the CPU 41 in the electronic timepiece 1 of thefirst embodiment with the exception of the processing of steps S105,S107, and S108 being replaced with steps S105 a, S107 a, and S108 a. Thesame reference numerals are applied to the same processing, and thedescription is omitted.

According to the time information obtaining processing of the presentembodiment, after the minute synchronizing point is defined (step S104),the CPU 41 obtains the data and identifies the signals until the CPU 41judges that the data for 3 frames is obtained (step S105 a). Then, whenit is judged that the data for 3 frames is obtained (step S105 a,“YES”), the CPU 41 decodes and decrypts the code array of each frame toseparately obtain the time information (step S107 a). The CPU 41confirms the consistency of the obtained time information for the 3frames (step S108 a), and judges whether the consistency of the timeinformation is satisfied (step S109).

The noise measuring processing called and performed in the timeinformation obtaining processing is performed with the same processingprocedure as the noise measuring processing called in the timeinformation obtaining processing performed in the electronic timepiece 1of the first embodiment. However, a different value is set as thepredetermined number which is the condition for judgment in theprocessing of step S306. In other words, in the time informationobtaining processing of the present embodiment, all of the pieces of thetime information of each frame need to be obtained accurately.Therefore, the present embodiment receives influence of the noise moreeasily than the time information obtaining processing by the electronictimepiece 1 of the first embodiment. However, in the present embodimentalso, the noise may be mixed in the code not necessary for obtaining thetime information, or the timing when the noise is mixed may notinfluence the identification of the code. Therefore, it is possible toset the predetermined number to for example, about 3 or 4.

As described above, similar to the electronic timepiece 1 of the firstembodiment, according to the electronic timepiece 1 a of the secondembodiment, the CPU 41 obtains the signal demodulated by the radio wavereceiving section 34 and counts the number of changes of the signal bythe noise for each second of the signal. When the number of changescounted is equal to or more than a threshold or is 0, it is determinedto be a noise mixed term, and when the number of times determined to bea noise mixed term within 20 seconds is equal to or more than apredetermined number, it is judged that obtaining time information isdifficult at this point, and the reception of the standard radio wave iscanceled. Therefore, when there is a request to obtain accurate timeinformation successively from received data of a predetermined number offrames (here, 3 frames), it is possible to judge when it is difficult toobtain accurate time information considering the possibility that thenoise may be mixed in portions where it is allowable even if noise ismixed such as the marker code portion or the extended code portion, orthe possibility that the timing that the burst noise is mixed may not becrucial for identifying the code. When it is judged to be difficult, itis possible to promptly cancel reception of the radio wave and to reduceunnecessary consumption of electric power.

The present invention is not limited to the above embodiments andvarious modifications can be made.

For example, the above embodiments describe an example using JJY.Alternatively, it is possible to employ the present invention whenreceiving the standard radio wave using the amplitude modulation of thelong wavelength band in various countries such as WWVB of the UnitedStates, MSF of Great Britain, DCF 77 of Germany, and the like.

According to the above embodiments, the rising edge or the falling edgeof the binarized signal is counted after the demodulated signal isbinarized. However, it is possible to count the change in the signalequal to or more than a predetermined level in multi-valued data oranalog data.

According to the above embodiments, after the second synchronizing pointis defined, whether to cancel the reception of the radio wave isdetermined repeatedly every 20 seconds in the noise measuringprocessing. However, a predetermined interval may be provided betweendetermining the noise. Alternatively, the noise can be determinedoverlapping a portion (for example, 10 seconds).

According to the above embodiments, the rising edge or the falling edgeof the signal of each second is counted dividing at each secondsynchronizing point. However, synchronizing with the secondsynchronizing point is not necessary. In this case, the number of thefalling edges is not necessarily once in each divided term. Therefore,it is preferable that the judgment is made by the number of risingedges.

According to the above embodiments, the term is divided at 1 second,however, it is not necessary to divide at 1 second, and the presentinvention can be similarly applied when divided at 0.5 seconds or 2seconds.

According to the above embodiments, the number of terms in which noiseis mixed within 20 seconds is counted. However, the length of time canbe suitably adjusted. Statistically, it is possible to determine thenoise level more accurately by setting a longer period of time. However,it is possible to more promptly cancel the operation of reception and toreduce the consumption of electric power by setting a shorter period oftime.

In addition to the above, the details regarding the specificconfiguration, control content and procedure shown in the aboveembodiments can be suitably changed without leaving the scope of theinvention.

Although various exemplary embodiments have been shown and described,the invention is not limited to the embodiments shown. Therefore, thescope of the invention is intended to be limited solely by the scope ofthe claims that follow and its equivalents.

The entire disclosure of Japanese Patent Application No. 2012-266904filed on Dec. 6, 2012 including specification, claims, drawings andabstract are incorporated herein by reference in its entirety.

What is claimed is:
 1. A time information obtaining device whichreceives a radio wave including time information to obtain timeinformation, the time information obtaining device comprising: a noisedetermining section which determines whether noise mixed in ademodulated signal of a radio wave received within a predetermined unitof time is equal to or more than a predetermined threshold level; and areception cancelling section which cancels reception of the radio wavewhen a number of times that the noise determining section determinesthat the noise mixed in the signal is equal to or more than apredetermined level is included at a percentage equal to or more than apredetermined percentage within a set time including a plurality of theunits of time.
 2. The time information obtaining device according toclaim 1, wherein, the noise determining section includes: a signalchange counting section which counts a number of times the demodulatedsignal of the received radio wave changes to a signal level equal to ormore than a predetermined signal level in the unit of time; and a mixednoise determining section which determines whether the mixed noise isequal to or more than the threshold level when the counted number oftimes the signal level changes is outside a range of a preset number. 3.The time information obtaining device according to claim 2, furthercomprising, a binarizing section which binarizes the demodulated signalof the received radio wave based on a predetermined binarizing thresholdlevel, wherein, the signal change counting section counts a number oftimes the binarized demodulated signal changes.
 4. The time informationobtaining device according to claim 1, wherein, the unit of time isequal to a length of each code in a code string showing the timeinformation.
 5. The time information obtaining device according to claim2, wherein, the unit of time is equal to a length of each code in a codestring showing the time information.
 6. The time information obtainingdevice according to claim 3, wherein, the unit of time is equal to alength of each code in a code string showing the time information. 7.The time information obtaining device according to claim 1, wherein, thereception cancelling section repeatedly judges whether to cancel thereception of the radio wave based on a recent determining result ofmixed noise in the set time each time a predetermined amount of timepasses while the radio wave is received.
 8. The time informationobtaining device according to claim 2, wherein, the reception cancellingsection repeatedly judges whether to cancel the reception of the radiowave based on a recent determining result of mixed noise in the set timeeach time a predetermined amount of time passes while the radio wave isreceived.
 9. The time information obtaining device according to claim 3,wherein, the reception cancelling section repeatedly judges whether tocancel the reception of the radio wave based on a recent determiningresult of mixed noise in the set time each time a predetermined amountof time passes while the radio wave is received.
 10. The timeinformation obtaining device according to claim 4, wherein, thereception cancelling section repeatedly judges whether to cancel thereception of the radio wave based on a recent determining result ofmixed noise in the set time each time a predetermined amount of timepasses while the radio wave is received.
 11. The time informationobtaining device according to claim 1, further comprising: a codeidentifying section which identifies each code of a code string showingthe time information in the demodulated signal; and a majority decidingsection which decides one code by majority for each code which does notchange within the predetermined number of times according to the timeinformation, among a predetermined number of codes identified in a sameposition in code strings obtained a predetermined number of times equalto 3 or more.
 12. The time information obtaining device according toclaim 2, further comprising: a code identifying section which identifieseach code of a code string showing the time information in thedemodulated signal; and a majority deciding section which decides onecode by majority for each code which does not change within thepredetermined number of times according to the time information, among apredetermined number of codes identified in a same position in codestrings obtained a predetermined number of times equal to 3 or more. 13.The time information obtaining device according to claim 3, furthercomprising: a code identifying section which identifies each code of acode string showing the time information in the demodulated signal; anda majority deciding section which decides one code by majority for eachcode which does not change within the predetermined number of timesaccording to the time information, among a predetermined number of codesidentified in a same position in code strings obtained a predeterminednumber of times equal to 3 or more.
 14. The time information obtainingdevice according to claim 4, further comprising: a code identifyingsection which identifies each code of a code string showing the timeinformation in the demodulated signal; and a majority deciding sectionwhich decides one code by majority for each code which does not changewithin the predetermined number of times according to the timeinformation, among a predetermined number of codes identified in a sameposition in code strings obtained a predetermined number of times equalto 3 or more.
 15. The time information obtaining device according toclaim 7, further comprising: a code identifying section which identifieseach code of a code string showing the time information in thedemodulated signal; and a majority deciding section which decides onecode by majority for each code which does not change within thepredetermined number of times according to the time information, among apredetermined number of codes identified in a same position in codestrings obtained a predetermined number of times equal to 3 or more. 16.A radio-controlled timepiece comprising: a time information obtainingdevice according to claim 1; a time keeping section which counts presenttime; a time calibrating section which calibrates the present timecounted by the time keeping section based on time information obtainedby the time information obtaining device; and a time display sectionwhich displays the present time counted by the time keeping section in apredetermined format.
 17. A radio-controlled timepiece comprising: atime information obtaining device according to claim 2; a time keepingsection which counts present time; a time calibrating section whichcalibrates the present time counted by the time keeping section based ontime information obtained by the time information obtaining device; anda time display section which displays the present time counted by thetime keeping section in a predetermined format.
 18. A radio-controlledtimepiece comprising: a time information obtaining device according toclaim 3; a time keeping section which counts present time; a timecalibrating section which calibrates the present time counted by thetime keeping section based on time information obtained by the timeinformation obtaining device; and a time display section which displaysthe present time counted by the time keeping section in a predeterminedformat.
 19. A radio-controlled timepiece comprising: a time informationobtaining device according to claim 4; a time keeping section whichcounts present time; a time calibrating section which calibrates thepresent time counted by the time keeping section based on timeinformation obtained by the time information obtaining device; and atime display section which displays the present time counted by the timekeeping section in a predetermined format.
 20. A radio-controlledtimepiece comprising: a time information obtaining device according toclaim 7; a time keeping section which counts present time; a timecalibrating section which calibrates the present time counted by thetime keeping section based on time information obtained by the timeinformation obtaining device; and a time display section which displaysthe present time counted by the time keeping section in a predeterminedformat.